Semiconductor device and method of manufacturing the same

ABSTRACT

A semiconductor device includes at least one interlevel insulating film, a storage electrode, a capacitor insulating film, a plate electrode, and a protective film. The interlevel insulating film is arranged on a semiconductor substrate. The storage electrode is made of a metal material and arranged on the interlevel insulating film. The capacitor insulating film is made of an insulating metal oxide and arranged on the storage electrode. The plate electrode is made of tungsten nitride and arranged on the capacitor insulating film. The protective film is arranged on the plate electrode to suppress outward diffusion of nitrogen from the plate electrode. A method of manufacturing the semiconductor device is also disclosed.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a semiconductor device with acapacitor using tungsten nitride as a material to form an electrode, anda method of manufacturing the same.

[0002] In a dynamic random access memory (DRAM) comprised of onetransistor and one capacitor, along with an increase in integrationdegree of the integrated circuit, it is required to increase the memorycapacity by reducing the memory cell area. In this requirement, atechnique has been proposed which increases the substantial area byforming a capacitor with a cylindrical or multilayered electrodestructure, so that the memory capacity is increased without increasingthe memory cell size.

[0003] For example, when a cylindrical capacitor structure is to beemployed, a plate electrode which forms a capacitor is formed on acapacitor film having a large step. A conductor layer serving as theplate electrode to be formed on the capacitor film must be formedcontinuously including a step portion produced by the thickness portionof the capacitor film. Tungsten nitride, titanium nitride, ruthenium, orthe like that can be formed with a good step coverage is used as thematerial of the conductor film, because these conductive materials canform a film by chemical vapor deposition (CVD) having a good stepcoverage. Among these conductive materials, tungsten nitride is superiorin terms of adhesion properties and easiness to be processed to theelectrode, and low leakage. Tungsten nitride is less expensive andeasier to be processed to the electrode than ruthenium. Also, tungstennitride can form a film with less damaging to an underlying capacitorfilm than titanium nitride.

[0004] A DRAM using above tungsten nitride will be described.

[0005] As shown in FIG. 7, a gate electrode 704 is formed on that regionon a semiconductor substrate 701, which is defined by an isolationregion 702 through a gate insulating film 703. Impurity regions areformed in the semiconductor substrate 701 on the two sides of the gateelectrode 704 by ion implantation or the like using the gate electrode704 as a mask, thereby forming source/drain regions 705.

[0006] An interlevel insulating film 706 is formed on the gate electrode704 over the entire surface of the semiconductor substrate 701. Acontact plug 707 to be connected to the corresponding source/drainregion 705 formed in the semiconductor substrate 701 is formed at apredetermined position of the interlevel insulating film 706. A bit line708 is formed to be connected to the contact plug 707.

[0007] An interlevel insulating film 709 is formed on the interlevelinsulating film 706 including the bit line 708. A contact plug 710 to beconnected to the corresponding source/drain region 705 formed in thesemiconductor substrate 701 is formed to extend through the interlevelinsulating films 709 and 706. A storage electrode 711 is formed on thecontact plug 710 through a barrier film 710 a.

[0008] A capacitor insulating film 712 is formed to cover the storageelectrode 711, and a plate electrode 713 made of tungsten nitride isformed to cover the storage electrode 711 and capacitor insulating film712.

[0009] In this manner, a transistor comprised of the gate electrode 704,and a capacitor to be connected to this transistor and comprised of thestorage electrode 711, capacitor insulating film 712, and plateelectrode 713 make up the basic unit of the memory cell.

[0010] An interlevel insulating film 714 made of an insulator is formedalso on the interlevel insulating film 709 including the plate electrode713. Although not shown, an interconnection layer to be connected to thebit line 708 and plate electrode 713 (described above) is formed on theinterlevel insulating film 714.

[0011] In the above semiconductor device, after the interlevelinsulating film is formed on the plate electrode, for example, when acontact between the interconnection formed on the interlevel insulatingfilm on the plate electrode and the silicon substrate is to be formed,high-temperature annealing at approximately 600° C. is sometimesperformed. If such a high temperature is applied, cracking may occur inthe plate electrode or in the worst case, the plate electrode may bepeeled.

SUMMARY OF THE INVENTION

[0012] It is, therefore, the principal object of the present inventionto provide a method of manufacturing a semiconductor device, by whicheven if a high temperature is applied in the post-process to a tungstennitride electrode which forms a capacitor, cracking or peeling will notoccur in the electrode.

[0013] In order to achieve the above object, according to the presentinvention, there is provided a semiconductor device comprising at leastone interlevel insulating film arranged on a semiconductor substrate, afirst electrode made of a metal material and arranged on the interlevelinsulating film, a capacitor insulating film made of an insulating metaloxide and arranged on the first electrode, a second electrode made oftungsten nitride and arranged on the capacitor insulating film, and aprotective film arranged on the second electrode to suppress outwarddiffusion of nitrogen from the second electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is a sectional view schematically showing the arrangementof a semiconductor device according to the present invention;

[0015]FIGS. 2A to 6L are sectional views showing the steps in a methodof manufacturing the semiconductor device shown in FIG. 1; and

[0016]FIG. 7 is a schematical sectional view showing the arrangement ofa conventional semiconductor device.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0017] An embodiment of the present invention will be described withreference to the accompanying drawings.

[0018]FIG. 1 shows a semiconductor device according to an embodiment ofthe present invention. Referring to FIG. 1, a gate electrode 104 isformed on that region on a semiconductor substrate 101, which is definedby an isolation region 102 through a gate insulating film 103. In FIG.1, impurity regions are formed in the semiconductor substrate 101 on thetwo sides of the gate electrode 104 by diffusion with ion implantationor the like using the gate electrode 104 as a mask, thereby formingsource/drain regions 105.

[0019] An interlevel insulating film 106 is formed over the entiresurface of the semiconductor substrate 101 including the gate electrode104. A contact plug 107 to be connected to the correspondingsource/drain region 105 formed in the semiconductor substrate 101 isformed at a predetermined position of the interlevel insulating film106. The contact plug 107 is connected to a bit line 108 arranged on theinterlevel insulating film 106.

[0020] An interlevel insulating film 109 is formed on the interlevelinsulating film 106 including the bit line 108. A contact plug 110 to beconnected to the corresponding drain/source region 105 formed in thesemiconductor substrate 101 is formed to extend through the interlevelinsulating films 109 and 106. A storage electrode 111 is formed on thecontact plug 110 through a barrier film 110 a.

[0021] A capacitor insulating film 112 is formed to cover the storageelectrode 111, and a plate electrode 113 made of tungsten nitride isformed to cover the storage electrode 111 and capacitor insulating film112. A transistor comprised of the gate electrode 104, and a capacitorto be connected to this transistor and comprised of the storageelectrode 111, capacitor insulating film 112, and plate electrode 113,each of which is described above, make up the basic unit of the memorycell.

[0022] In this embodiment, a protective film 113 a made of a metalsilicide such as tungsten silicide is formed to cover the upper surfaceof the plate electrode 113. An interlevel insulating film 114 made of aninsulator is formed also on the interlevel insulating film 109 includingthe plate electrode 113. Although not shown, an interconnection layer tobe connected to the bit line 108 and plate electrode 113 (describedabove) is formed on the interlevel insulating film 114.

[0023] As described above, since the protective film 113 a made of themetal silicide is formed on the upper surface of the plate electrode113, even if high-temperature annealing at, e.g., 600° C. or more isperformed in the post-process, cracking in the plate electrode 113 canbe suppressed.

[0024] The above problem of cracking in the plate electrode is supposedto occur because, during the high-temperature annealing in thepost-process, nitrogen is diffused outward from tungsten nitride thatforms the plate to cause shrinkage of the plate electrode. This outwarddiffusion of nitrogen can be suppressed by the above protective filmmade of the metal silicide, so cracking or the like in the plateelectrode can be suppressed. It is supposed that outward diffusiondescribed above is suppressed in the following manner. When a metalsilicide film is formed on tungsten nitride, when annealing exceeding atleast 600° C. is performed, a dense thin film made of a nitride of themetal silicide is formed at the interface between tungsten nitride andthe metal silicide film, thereby suppressing outward diffusion ofnitrogen from the plate electrode.

[0025] A manufacturing method will be described.

[0026] A method of manufacturing a semiconductor device with thestructure shown in FIG. 1 will be described with reference to FIGS. 2Ato 6L. First, as shown in FIG. 2A, a gate electrode 104 is formed by aknown method on that region on a silicon substrate 101, which is definedby an isolation region 102 through a gate oxide film 103. After the gateelectrode 104 is formed, source/drain regions 105 are formed by ionimplantation or the like using the gate electrode 104 as a mask.

[0027] As shown in FIG. 2B, an interlevel insulating film 106 made of aninsulator such as silicon oxide is formed on the entire region of thesilicon substrate 101. A contact plug 107 to be connected to either oneof the source/drain regions 105 formed in the semiconductor substrate101 is formed at a predetermined position. A bit line 108 is formed tobe connected to the contact plug 107.

[0028] As shown in FIG. 3C, an interlevel insulating film 109 made of aninsulator such as silicon oxide is formed on the interlevel insulatingfilm 106 including the bit line 108. As shown in FIG. 3D, a contact hole301 is formed in the interlevel insulating films 109 and 106 by theknown photolithography or etching technique to reach the correspondingsource/drain region 105.

[0029] Subsequently, polysilicon is deposited on the interlevelinsulating film 109 so as to fill the contact hole 301, thereby forminga polysilicon film 302 as shown in FIG. 3E. Polysilicon may be depositedby, e.g., CVD.

[0030] The polysilicon film 302 is selectively etched back so a contactplug 110 made of polysilicon is formed in the contact hole 301 whilekeeping a certain space in the upper portion of the contact hole 301, asshown in FIG. 3F. Selective etch-back of the polysilicon film 302 may beperformed by reactive dry etching using an etching gas that has aselectivity with respect to silicon and does not substantially etch theinterlevel insulating film 109.

[0031] As shown in FIG. 4G processes such as film formation and CMP oretch-back are performed to form a barrier film 110 a to cover the uppersurface of the contact plug 110.

[0032] As shown in FIG. 4H, a metal film 401 made of, e.g., ruthenium,is formed on the interlevel insulating film 109 including the barrierfilm 110 a by, e.g., sputtering or CVD, to a thickness of about 20 nm to100 nm.

[0033] The metal film 401 is patterned by the known photolithography andetching techniques to form a storage electrode (first electrode) 111 onthe interlevel insulating film 109 so as to be connected to the contactplug 110 through the barrier film 110 a, as shown in FIG. 4I. Thematerial of the storage electrode is not limited to ruthenium, but goldor platinum may also be used instead.

[0034] A tantalum oxide film is formed on the interlevel insulating film109 to a thickness of about 5 nm to 20 nm to cover the storage electrode111, and is subjected to the post-process by, e.g., annealing in anoxygen atmosphere at a temperature of approximately 500° C. to 700° C.,to form a capacitor insulating film 112, as shown in FIG. 5J. Thematerial of the capacitor insulating film is not limited to tantalumoxide, but other metal oxides may also be used instead.

[0035] A conductive film made of, e.g., tungsten nitride, is formed onthe capacitor insulating film 112 to a thickness of about 10 nm to 30 nmand, for example, a tungsten silicide film is successively formed to athickness of about 5 nm to 20 nm. These two films are patterned by theknown photolithography and etching techniques, thereby forming a plateelectrode (second electrode) 113 with an upper surface being covered bya protective film 113 a, as shown in FIG. 5K.

[0036] Formation of the tungsten nitride film and formation of thetungsten silicide film described above are preferably performedcontinuously in a single apparatus by thermal chemical vapor deposition(thermal CVD). First, using WF₆ as the tungsten source gas and NH₃ asthe nitrogen source gas, and setting the substrate temperature toapproximately 500° C., a tungsten nitride film is formed. Successively,using SiH₄, in place of NH₃, as the silicon source gas, tungstensilicide is formed on the formed tungsten nitride film. When filmformation is continuously performed in this manner, a native insulatinglayer or the like will not be formed at the interface between thetungsten nitride film and tungsten silicide.

[0037] After that, an interlevel insulating film 114 made of aninsulating material such as silicon oxide is formed to cover the plateelectrode 113, thereby forming a 1-transistor, 1-capacitor DRAM, asshown in FIG. 6L.

[0038] In the above description, tungsten silicide is used as thematerial of the protective film. However, the present invention is notlimited to this, and other metal suicides may be used. If a siliconnitride film is used as the protective film, the same effect can beobtained.

[0039] In the above embodiment, the capacitor electrode forms a flatplate. If the capacitor has a cylindrical or multilayered electrodestructure, the present invention can be applied in the same manner as inthe above embodiment. When the capacitor electrode is cylindrical, aplate electrode—capacitor insulating film—storage electrode—capacitorinsulating film—plate electrode are arranged in it in this order on theside surface from the outer side. Alternatively, the capacitor can havea multilayered electrode structure. In this case, a storage electrode issometimes arranged at the uppermost layer.

[0040] As has been described above, according to the present invention,an interlevel insulating film is formed on a semiconductor substrate, afirst electrode made of a metal material is formed on the interlevelinsulating film, a capacitor insulating film made of an insulating metaloxide is formed on the first electrode, a second electrode made oftungsten nitride is formed by chemical vapor deposition on the surfaceof the first electrode while being insulated and isolated by thecapacitor insulating film, and a protective film is formed on the secondelectrode to suppress outward diffusion of nitrogen from the secondelectrode.

[0041] According to the present invention, the protective film is formedon the second electrode. After the protective film is formed, nitrogenis suppressed from being outwardly diffused from tungsten nitride thatforms the second electrode, and a change in volume of the secondelectrode by outward diffusion of nitrogen is suppressed. As a result,according to the present invention, even if high-temperature heat isapplied in the post-process to the tungsten nitride electrode that formsthe capacitor, cracking or peeling of the electrode can be suppressed,which is an excellent effect.

What is claimed is:
 1. A semiconductor device comprising: at least oneinterlevel insulating film arranged on a semiconductor substrate; afirst electrode made of a metal material and arranged on said interlevelinsulating film; a capacitor insulating film made of an insulating metaloxide and arranged on said first electrode; a second electrode made oftungsten nitride and arranged on said capacitor insulating film; and aprotective film arranged on said second electrode to suppress outwarddiffusion of nitrogen from said second electrode.
 2. A device accordingto claim 1, wherein said protective film is made of a metal silicide. 3.A device according to claim 2, wherein said protective film is made oftungsten silicide.
 4. A device according to claim 1, wherein saidprotective film is made of silicon nitride.
 5. A device according toclaim 1, wherein a transistor is arranged on said semiconductorsubstrate under said interlevel insulating film.
 6. A method ofmanufacturing a semiconductor device, comprising the steps of: formingat least one interlevel insulating film on a semiconductor substrate;forming a first electrode made of a metal material on the interlevelinsulating film; forming a capacitor insulating film made of aninsulating metal oxide on the first electrode; forming a secondelectrode made of tungsten nitride, formed by thermal chemical vapordeposition, on the capacitor insulating film; and forming a protectivefilm on the second electrode to suppress outward diffusion of nitrogenfrom the second electrode.
 7. A method according to claim 6, wherein theprotective film is made of a metal silicide.
 8. A method according toclaim 7, wherein the protective film is made of tungsten silicide.
 9. Amethod according to claim 6, wherein the protective film is made ofsilicon nitride.
 10. A method according to claim 6, wherein theprotective film is formed by thermal chemical vapor deposition using atleast silicon source gas.
 11. A method according to claim 6, wherein atungsten nitride film and a silicon-containing thin film arecontinuously formed on the semiconductor substrate on which thecapacitor insulating film has been formed, and the tungsten nitride filmand the silicon-containing thin film are processed to form the secondelectrode and the protective film.